1. Field of the Invention
The present invention relates to a structure of a MEMS (micro electro mechanical systems) switch.
2. Description of the Related Art
MEMS is also called a “micro machine” or a “MST (micro system technology)” and refers to a system in which a minute mechanical structure and an electric circuit formed of a semiconductor element are combined. A microstructure has a three-dimensional structure which is partially movable in many cases, unlike a semiconductor element such as a transistor. An electric circuit controls motion of a microstructure or receives and processes a signal from the microstructure. Such a micro machine formed of a microstructure and an electric circuit can have a variety of functions: for example, a sensor, an actuator, and a passive element such as an inductor or a variable capacitor.
A microstructure characterizing a micro machine includes a structural layer having a beam structure in which an end portion thereof is fixed to a substrate and a vacant space between the substrate and the structural layer. A microstructure in which the structural layer is partially movable since there is a space can realize a variety of functions one of which is a switch. A MEMS switch formed of a microstructure is turned on or off with or without physical contact unlike a field-effect switching transistor and thus has advantages such as good isolation when it is off and less insertion loss when it is on.
Further, a MEMS includes not only a microstructure but an electric circuit in many cases; therefore, it is preferable that it can be manufactured applying a process the same as or similar to that of a semiconductor integrated circuit. In the present invention, described is a MEMS switch utilizing a surface micromachine technology for manufacturing a structure with a stack of thin films.
A MEMS switch includes a bridge structure (structural layer) over a substrate and two or more pairs of electrodes facing each other on a surface of the substrate and the substrate side of the bridge structure. By applying a voltage to one pair of electrodes, the bridge structure is pulled down to the substrate side by an electrostatic attractive force and the other pair of electrodes physically come in contact with each other, so that the MEMS switch is turned on (Patent Document 1: Japanese Translation of PCT International Application No. 2005-528751 and Patent Document 2: Japanese Published Patent Application No. 2003-217423).
Further, in order to prevent contact between a pair of electrodes to which a voltage is applied, a stopper for limiting a movable region of a structural layer (also referred to as a bumper or a bump) is generally formed (Patent Document 1).